Sealing construction for a suction box of a suction roll in a paper machine and method in sealing operation of a suction roll

Abstract: The invention concerns a sealing construction for a suction box of a suction roll in a paper machine and a method in sealing operation of a suction roll. The sealing construction comprises a seal (10) provided in a holder (11) and loading means, preferably at least one loading hose (12a,12b) between the holder (11) and the seal (10). The seal (10) is pressed against the inner face (T') of the roll mantle of the suction roll (T) by means of the pressure of a medium that has been supplied into the loading hose. There are locking means (13) between the seal (10) and the holder (11), by means of which locking means the seal (10) can be locked in the desired position.

Description: The invention concerns a suction roll according to the preamble of Claim 1 and a method of sealing a suction box of a suction roll according to the preamble of Claim 13. The preambles of Claims 1 and 13 are based on the disclosure of DE-A-1 146 350. The wear of the seals in suction rolls has become a problem in an attempt to achieve longer servicing intervals. In a prior-art construction, in view of producing an efficient and well sealed suction roll, the seals are pressed pneumatically against the inner face bf the roll mantle of the roll. In such a case, the compression force is maintained constantly, and the seal is worn rapidly. In the present application, an efficient solution is described for avoiding the wear of the seal. According to the present invention, the seal rib is provided with locking means. The seal is first pressed against the roll mantle. After the negative pressure has been developed in the suction box, the seal is locked in its holder. Finally, the pressure can be discharged from the loading means of the seal. When an arrangement in accordance with the invention is used, even the water lubrication can be omitted. Moreover, the seals may be provided with chamfering, which permits gradual equalization of the pressures in the perforations in the suction roll as the perforations in the roll depart from the zone of negative pressure while the roll revolves. The suction roll in accordance with the present invention is mainly characterized by the features defined in the characterizing portion of Claim 1. On the other hand, the method of sealing the suction box of a suction roll in accordance with the present invention is mainly characterized by the features defined in the characterizing portion of Claim 13. In the following, the invention will be described with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embodiments alone. Figure 1A is an illustration of a suction roll in a paper machine, by means of which suction roll water is removed out of the web. Figure 1B shows a seal holder for prior-art sealing operation and a loading hose placed on the bottom of said holder. Figure 1C is a sectional view taken along the line I-I in Fig. 1B. Figure 2 shows a novel seal construction in accordance with the present invention, which comprises seal locking means. Figure 3A shows a second embodiment, in which the locking is accomplished exclusively by means of a loading hose, which is fitted in a longitudinal groove in the seal. Figure 3B shows a construction in accordance with the invention, in which the seal is fitted in a separate intermediate holder, which is displaceable by means of loading hoses, a spring load being provided between the intermediate holder and the seal, and in which construction the locking takes place so that the intermediate holder is locked in relation to the socket proper. Figure 3C shows an embodiment of the invention which is in the other respects similar to the embodiment shown in Fig. 2, except that in this construction there is only one loading hose placed on the bottom of the seal. Figures 3D and 3E show the use of a wedge-shaped locking piston. Fig. 3D illustrates a situation in which the loading is on but in which locking has not been carried out. Fig. 3E illustrates a situation in which the locking is on and in which the load has been removed from the seal. Figure 3F shows an embodiment of the invention in which both a loading hose and a U-section locking piston are placed in a groove in the seal. Figure 3G shows an embodiment of the invention in which the locking is carried out by means of the spring force of a spring. Figure 4 shows a pneumatic diagram of the control of the seal. Fig. 1A shows a prior-art operation of a suction roll in a paper machine. The web R is passed through the nip N 1 between the rolls T 1 and T 2 along the face of the roll T 2 into the nip N 2 between the rolls T 2 and T 3 . In the interior of the roll T 2 , there are a vacuum chamber A 1 and a vacuum chamber A 2 . The vacuum chamber A 1 is placed between the seals C 1 and C 2 , and the vacuum chamber A 2 between the seals C 2 and C 3 . Thus, water is sucked out of the web R into the vacuum chambers A 1 ,A 2 . In said prior-art operation, the seals C 1 ,C 2 and C 3 are pressed constantly against the inner face of the roll T 2 mantle T' by means of a force produced by loading hoses. Fig. 1B shows a prior-art holder construction 11 for the seals C 1 ,C 2 and C 3 shown in Fig. 1A. The seal (not shown in the figure) is pressed with force, by means of the pneumatic pressure produced into the loading hose 12, against the inner face T' of the roll mantle of the roll T 2 . Fig. 1C is a sectional view taken along the line I-I in Fig. 1B. In the prior-art solutions shown in Figs. 1A...1C, the seals C 1 ,C 2 and C 3 are pressed constantly with a force against the inner face of the roll mantle of the revolving roll. The seals C 1 ,C 2 and C 3 are worn rapidly even if they were lubricated with water during the operation of the roll. Fig. 2 shows a solution in accordance with the invention for prevention of wear of the seal. In the way shown in the figure, the seal 10 comprises loading hoses 12a and 12b in the grooves U 1 and U 2 in the holder 11. By means of pneumatic pressure introduced into the loading hose 12a,12b, the hose 12a,12b is inflated between the seal 10 bottom and the grooves U 1 and U 2 whereby the seal 10 is pressed by means of the loading hose with force against the inner face T' of the roll mantle of the suction roll T. When the load is on in the hoses 12a and 12b, negative pressure is sucked into the space A 1 , after which, according to the invention, the seal 10 is locked in its position in relation to its holder 11 by means of the locking means 13. After this, the pressure is removed from the loading hoses 12a,12b, whereby the wear of the seals 10 is also eliminated. By means of the locking member 13, preferably a loading hose 14, the seal 10 is kept in a position in which adequate negative pressure is maintained in the vacuum space A 1 between the longitudinal seals at the edges of the suction box in the suction roll. The locking of the seal 10 takes place so that the locking means 13 of the seal 10 are affected preferably by means of pneumatic pressure applied to a third loading hose 14, and the locking piston 15 is displaced by means of said third loading hose 14. The piston 15 presses the seal 10 against the other inside wall 16a 2 of the seal holder 11. The loading hose 14 and the connected piston 15 are placed in the groove M in the side wall 16a 1 in the holder 11. In the way shown in the figure, the seal is provided with a chamfering 17 at its edge. By means of the chamfering 17, the negative pressure in the perforations Ta 1 ,Ta 2 ... in the suction roll T is equalized gradually, and intensive disturbing noise is prevented in connection with equalization of the pressure as the perforations Ta 1 ,Ta 2 ... in the roll T pass, along with the rotation of the roll, from the area of negative pressure to the area of normal atmospheric pressure. Fig. 3A shows an embodiment of the invention in which the locking means 13 of the seal 10 consist of a loading hose 14 alone. The loading hose 14 is fitted in a groove C of semicircular section formed in the side face 10a 1 of the seal 10. Thus, the seal is fitted to act between the holder 11 wall 16a 1 and the groove C face C'. When the loading pressure is passed into the hose 14, the seal 10 is pressed against the wall 16a 2 of the holder 11. In the embodiments of both Fig. 2 and Fig. 3A, the holder comprises a guide projection E in the area of the centre axis Y of the holder, the cross-sectional shape of said projection corresponding to the shape of the groove F in the bottom of the seal. The loading hoses 12a,12b are placed in the spaces U 1 and U 2 between the guide projection F and the walls 16a 1 ,16a 2 . Fig. 3B shows an embodiment of the invention in which the seal 10 is fitted in an intermediate holder 18 displaceable by means of loading hoses 12a,12b. In its bottom, the intermediate holder comprises a groove F, which is fitted onto the guide projection E placed on the central axis Y of the holder 11 and having a corresponding cross-sectional shape. The loading hoses 12a and 12b are placed in the grooves U 1 ,U 2 between the projection E and the side walls 16a 1 ,16a 2 of the socket 11. In a way similar to the embodiment shown in Fig. 2, the locking means 13 of the seal 10 consist of a loading hose 14 and a locking piston 15. The locking piston 15 is pressed against the face 18a 1 of the intermediate socket 18. The loading hose 14 and the connected locking piston 15 are fitted in the groove M that has been formed into the wall 16a 1 of the holder 11. In the embodiment shown in Fig. 3B, the cross-sectional profile of the seal 10 is a T-section, the so-called flange part 10b of the section being placed in a backed-off groove G placed on the top face of the intermediate holder 18. On the bottom of the groove, there is a spring J, by whose means the seal 10 is pressed by the intermediate of its flange 10b against the walls 19a 1 ,19a 2 above the groove G. The arrangement of an intermediate holder equalizes the effects of any swinging movement of the inner face of the mantle. Fig. 3C shows an embodiment in which a seal 10 loading hose 12 is placed on the bottom of the groove U in the seal 10 holder 11. The locking arrangement of the seal 10 is similar to that shown in the embodiment of Fig. 2. The seal is locked by means of the locking means 13 by acting upon the other loading hose 14 and by shifting the locking piston 15 connected with the loading hose 14 against the side face 10a 1 of the seal 10, whereby the other wall 10a 2 of the seal is also pressed against the other inner vertical face 16a 2 of the groove U in the holder 11. Fig. 3D shows an embodiment of the invention in which a wedge-shaped locking piston 15 is used. The loading hose 14 in the groove M in the holder acts with a force upon the wedge-shaped loading piston 15, and at the opposite side, in the groove M' in the holder, there is a wedge-shaped opposite locking piston 150. When the loading hose 14 is activated, the locking pistons 15,150 are displaced to the side and slightly downwards by means of the wedge-shaped faces that are slightly downwards inclined, compared with a horizontal plane, and that are placed in the grooves M,M' and on the locking pistons 15,150, and the seal 10 is pressed slightly apart from the inner face of the roll mantle. Fig. 3D illustrates a situation in which locking has not been performed, and Fig. 3E illustrates a case in which the seal 10 is guided slightly apart from the roll mantle face by means of the wedge faces g 1 and g 2 of the locking pistons 15,150. Said movement to the side and downwards has been permitted by allowing a certain play to remain between the faces in the grooves M,M' and the faces on the locking pistons and/or by also using resilient seal pieces S 1 ,S 2 ... In Fig. 3F, an embodiment of the invention is shown in which a loading member, preferably a loading hose 14, is placed in the groove C in the seal 10, and additionally, in the rectangular section in said groove C, a U-section piston part 15 is fitted, the loading hose 14 being at least partly placed inside the U-section of said piston part. Fig. 3G shows an embodiment of the invention in which the spring J 2 carries out the locking by pressing the piston 15 against the side face of the seal 10 and by thereby pressing the seal 10 against the wall face 16a 1 of the holder. The locking force of the spring J 2 has been dimensioned such that it does not prevent movement of the seal 10 performed by means of the loading hoses 12a and 12b, but the spring force of the spring is sufficient to keep the seal 10 against the wall face 16a 1 of the holder and against the inner face of the roll mantle after elimination of the loading pressure of the loading hoses 12a,12b. Fig. 4 shows a pneumatic diagram of the sealing operation in accordance with the invention. The compressed air out of the line O is passed into the branch line O 1 ,O 2 through the directional valves V 1 ,V 2 to the seal 10. The loading of the seals 10 is controlled through the line O 1 , and the locking of the seal 10 is controlled through the line O 2 . After a sufficient negative pressure has been formed in the vacuum space in the suction box, the automatic system locks the seal in its position by means of the hose-loaded locking piston. At the same time, the automatic system removes the pressure from the loading hoses of the seal, whereby the force of loading of the seal against the mantle is gradually reduced to zero and the wear of the seal and of the inner face of the mantle is discontinued. If the negative pressure in the suction zone is reduced, e.g., during a web break, the automatic system switches off the locking and switches on the pressure into the loading hoses, which guarantees maintenance of the negative pressure also in situations of disturbance.

Claims: Suction roll for a paper machine, said suction roll comprising a perforated roll mantle and an internal suction box for applying negative pressure to a part of the inner face of said roll mantle, said suction box defining a vacuum space (A 1 , A 2 ) sealed on its edges by a sealing structure comprising a seal (10) provided in a holder (11), said seal (10) having a sealing face which is pressed against the inner face of said roll mantle, at least one loading hose (12a, 12b) provided between said holder (11) and said seal (10), whereby said seal (10) is pressed against the inner face (T') of said roll mantle by means of the pressure of a medium supplied into said loading hose (12a, 12b), characterized by locking means (13) provided between said seal (10) and said holder (11) by means of which locking means (13) said seal (10) can be locked in a desired position, whereby it is possible to remove the load from said loading hose (12a, 12b) so as to minimize the wear of said seal (10). Suction roll as claimed in claim 1, characterized in that said locking means (13) consists of a loading hose (14). Suction roll as claimed in claim 2, characterized in that said loading hose (14)is placed in a groove (M) or equivalent provided in a side face (16a1) of said holder (11) of said seal (10). Suction roll as claimed in claim 2 or 3, characterized in that said holder (11) has side walls (16a 1 , 16a 2 ) forming a groove in said holder (11) in which said seal (10) is provided, and in that said seal (10) has side walls (10a 1 , 10a 2 ), and in that said loading hose (14) is connected with a locking piston (15) being fitted to act upon one side wall (10a 1 ) of said seal (10) so that said other side wall (10a 2 ) of said seal (10) is pressed with force against the side wall (16a 2 ) of said holder (11). Suction roll as claimed in any of the preceding claims 2 to 4, characterized in that said holder (11) has side walls (16a 1 , 16a 2 ) forming a groove in said holder (11) in which an intermediate holder (18) is placed, and in that said intermediate holder (18) comprises a groove (G) in which said seal (10) is placed, said intermediate holder (18) being pressed against one side face (16a2) of said holder (11) by said loading hose (14) being placed between said intermediate holder (18) and said holder (11). Suction roll as claimed in the preceding claim, characterized in that said seal (10) comprises a flange portion (10b) with a wider cross-section, said groove (G) comprises walls (19a1, 19a2) forming an undercut so that said flange portion (10b) is inserted into said groove (G), a spring (J) is provided between a bottom face of said groove (G) and said flange portion (10b) thereby pressing said flange portion (10b) against said walls (19a1, 19a2) of said undercut. Suction roll as claimed in any of the claims 2 and 4 to 6, characterized in that said loading hose (14) is placed in a groove (C) provided in a side face (10a 1 ) of said seal (10). Suction roll as claimed in the preceding claim, characterized in that said loading hose (14) is connected with a locking piston (15) being placed in said groove (C), whereby said groove (C) is preferably of rectangular cross-shape, and being adapted to act upon one side wall (10a 1 ) of said holder (11) so that said seal (10) is pressed with force against the other side wall (16a 2 ) of said holder (11). Suction roll as claimed in claim 4, characterized in that wedge-shaped faces which are slightly inclined downwards, compared with a horizontal plane, are formed in said groove (M) and on said locking piston (15) so that said seal (10) is guided slightly apart from the inner face of said roll mantle when the loading hose (14) is activated in a locking situation. Suction roll as claimed in the preceding claim, characterized by comprising further wedge-shaped faces which are slightly inclined downwards, compared with a horizontal plane, which are placed in a further groove of said holder (11) being provided at the inner side face opposite said groove (M) and on a further locking piston (150) so that said seal (10) is clamped between both locking pistons (15, 150) in a locking situation, whereby said seal (10) is slightly separated from the inner face (T') of said roll mantle. Suction roll as claimed in claim 1, characterized in that said locking means (13) is a spring (J2) which is fitted to act upon said seal (10) to lock it in its holder (11). Suction roll as claimed in the preceding claim, characterized in that said spring (J2) is fitted in a groove (M) in said holder (11), and said spring (J2) is fitted to act upon said seal (10) through a piston (15) being fitted between said spring (J2) and said seal (10). Method of sealing a suction box of a suction roll having a perforated roll mantle, said suction box defining a vacuum space (A1) in its interior sealed on its edges by a sealing structure comprising a seal (10) provided in a holder (11), by pressing said seal (10) with a force against the inner face (T') of said roll mantle during the formation of negative pressure in said vacuum space (A1), characterized in that there is at least one seal (10) which can be locked in relation to said holder (11) and in that said seal (10) is locked in its position after the negative pressure has been generated in said vacuum space (A1), and in that the force pressing said seal (10) against the inner face (T') of said roll mantle is withdrawn after said seal (10) is locked in relation to its holder (11) so as to minimize the wear of said seal (10). Method as claimed in the preceding claim, characterized in that the locking of said seal (10) takes place by pressing said seal (10) or a part operationally connected with it, preferably an intermediate holder (18), against said holder (11). Method as claimed in claims 13 or 14, characterized by using a loading hose (14) for the locking of said seal (10), said loading hose (14) being loaded by means of compressed air. Method as claimed in claim 15, characterized in that said loading hose (14) is fitted between a side face of said seal (10) and a side face of said holder (11) in which said seal (10) is provided or between a side face of said intermediate holder (18) in which said seal (10) is provided and said side face of said holder (11). Method as claimed in the preceding claim, characterized in that said seal comprises a flange portion (10b) having a wider cross-section which is inserted into a groove (G) provided in said intermediate holder (18), said groove (G) having an undercut which is formed by walls (19a1, 19a2), said flange portion (10b) is pressed against said walls (19a1, 19a2) of said undercut by means of a spring (J) which is provided between a bottom face of said groove (G) and said flange portion (10b).

Inventors: SNELLMAN JORMA, SNELLMAN, JORMA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F3
IPC codes: D21F3